Polypropylene is cheap, excellent in rigidity, humidity resistance and heat resistance, and also superior in moldability. So, using these properties, nonwoven fabrics have been produced in large quantities and begun to be used for various applications including sanitary materials.
However, propylene has properties such that the rigidity is high but stretch properties are not sufficient so that it has been considered that a nonwoven fabric composed of polypropylene could not be used in the field requiring stretch properties and a small residual stain. When such stretch properties are required, thermoplastic polyurethane has hitherto been used in many cases (Patent Document 1).
By using a soft polyolefin instead of polyurethane (Patent Document 2), a prescribed improvement has been exhibited but there have been problems such that surface appearance of a mold product is poor and sense of touch is also poor for the applications requiring stretch properties as described above.
Furthermore, a soft polyolefin and an isotactic polypropylene are continuously polymerized (Patent Document 3) to be used for an elastic fiber in some cases, whereas the mixture ratio of the soft polyolefin and isotactic polypropylene, and an effect on stretch properties are not clearly shown.
Further, when a blend composition of the soft polyolefin and low viscosity homopolypropylene with high MFR (250 to 550) are processed into a fiber or the like, processability and flexibility (drape property) are obtained (Patent Document 4). However, there is no description of stretch properties.
On the other hand, when a copolymer having a component unit composed of styrene is used, stretch properties are excellent, but rigidity is not sufficiently exhibited and adhesiveness to a nonwoven fabric composed of polyolefin or a film composed of polyolefin is bad. Thus, when it is used as a sanitary material or the like, a problem in adhesion might be an obstacle, causing a problem in that it is not possible to freely design products.
Patent Document 1: WO 2002/65679 pamphlet
Patent Document 2: WO 1993/15251 pamphlet
Patent Document 3: WO 2003/040201 pamphlet
Patent Document 4: WO 2001/094462 pamphlet